Substrate holder for plasma processing

ABSTRACT

An improved substrate holder comprises an electrode supporting a focus ring and a substrate, an insulating member surrounding the electrode and focus ring, a ground member surrounding the insulating member, and a focus ring surrounding the substrate. The focus ring provides a RF impedance substantially equivalent to a RF impedance of the substrate. A method of processing a substrate utilizing the improved substrate holder reduces arcing between the edge of the substrate and the focus ring. The method comprises the steps of placing the focus ring on the electrode, placing the substrate on the electrode and processing the substrate. Additionally, a method of controlling a focus ring temperature and a substrate temperature utilizing the improved substrate holder comprises the steps of placing the focus ring on the electrode, placing the substrate on the electrode, clamping the focus ring and the substrate to the electrode using an electrostatic clamp, supplying heat transfer gas(es) to the space residing between the focus ring and the electrode, and the space between the substrate and the electrode, and controlling the temperature of the electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority and is related to U.S.application No. 60/363,284, filed on Mar. 12, 2002, the entire contentsof which are herein incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to substrate holders employed in plasmaprocessing and more particularly to an improved substrate holder forplasma processing.

2. Description of Related Art

One area of plasma processing in the semiconductor industry whichpresents formidable challenges is, for example, the manufacture ofintegrated circuits (ICs). Demands for increasing the speed of ICs ingeneral, and memory devices in particular, force semiconductormanufacturers to make devices smaller and smaller on the wafer surface.And conversely, while shrinking device sizes on the substrate isincurred, the number of devices fabricated on a single substrate isdramatically increased with further expansion of the substrate diameter(or processing real estate) from 200 mm to 300 mm and greater. Both thereduction in feature size, which places greater emphasis on criticaldimensions (CD), and the increase of substrate size lead to even greaterrequirements on plasma processing uniformity to maximize the yield ofsuperior devices.

One such consequence of non-uniform plasma processing can be, forexample, the unequal charging of the substrate surface in contact withthe plasma and the focus ring surrounding the substrate. Using currentfocus ring design practice, the surface potential of the focus ring canbe substantially different than the surface potential of the substrate.Subsequently, the difference in surface potential can lead to anon-uniform plasma sheath thickness and, therefore, result innon-uniform plasma properties proximate the substrate edge. Moreover,the difference in surface potential between the substrate edge and focusring can be sufficiently great to cause an electrical discharge (arc)arising in a catastrophic process failure and reduced device yield.

In a known plasma processing system, substrate arcing has been observedand can be attributable to the aforementioned focus ring design. Forexample, FIG. 1 presents a known substrate holder 1 comprising a RFbiasable electrode 10, electrode insulator 12, ground wall 14 withsurface anodization 16, and focus ring 18. The substrate holder 1further includes an electrostatic clamp (ESC) 20 in order to facilitateholding a substrate 22. Although, not shown in detail in FIG. 1, theelectrostatic clamp 20 typically comprises a clamp electrode encasedwithin a ceramic body. The focus ring 18 is generally fabricated from asilicon-containing material such as, for example, silicon or siliconcarbide, when processing silicon substrates. However, the material andsize of the focus ring 18 can result in a low capacitance orcorresponding high RF impedance leading to a surface potentialsubstantially greater than the surface potential of the substrate 22. Asa consequence, the plasma sheath 30 can be substantially non-uniform,comprising a thin region 32 above the focus ring 18, a thicker region 34above the substrate 22 and a transitional region 36 existingtherebetween.

As stated above, the potential difference associated with thenon-uniform plasma sheath can manifest as substrate arcing, hence,leading to catastrophic reduction in device yield. It is, therefore,desirable to achieve a uniform plasma sheath thickness across thesubstrate and the surfaces proximate the edge of the substrate.

An additional shortcoming of current focus ring design practice includesa substantially different temperature between the substrate and thefocus ring. In fact, it is not unrealistic to observe focus ringtemperatures exceeding the substrate temperature by more than severalhundred degrees centigrade. This observation is primarily attributableto the poor thermal contact between the focus ring and the temperaturecontrolled electrode. As a consequence, the “hot” focus ring can heatthe substrate edge leading to non-uniform substrate temperatures and,hence, non-uniform substrate processing particularly local to thesubstrate edge. It is, therefore, desirable to control the focus ringtemperature as well as the substrate temperature.

SUMMARY OF THE INVENTION

The present invention provides for an improved substrate holder for aplasma processing system in order to alleviate the aforementionedshortcomings of known substrate holders. The improved substrate holdercomprises an electrode supporting a focus ring and a substrate on anupper surface thereof, an insulating member surrounding the electrodeand focus ring, a ground member surrounding the insulating member, and afocus ring surrounding the substrate. The focus ring comprises a RFimpedance substantially equivalent to a RF impedance of the substrate.

It is a further object of the present invention to provide an improvedsubstrate holder further comprising an electrostatic clamp, wherein theelectrostatic clamp can serve as the upper surface of the electrode.

It is a further object of the present invention to provide an improvedsubstrate holder further comprising a heating and cooling system forcontrolling the temperature of the electrode.

The present invention further describes a method of processing asubstrate utilizing the improved substrate holder in order to minimizearcing between the edge of the substrate and the focus ring. The methodcomprises the steps of placing the focus ring on the electrode, placingthe substrate on the electrode and processing the substrate.

Additionally, the present invention describes a method of controlling afocus ring temperature and a substrate temperature utilizing theimproved substrate holder. The method comprises the steps of placing thefocus ring on the electrode, placing the substrate on the electrode,clamping the focus ring and the substrate to the electrode using anelectrostatic clamp, supplying heat transfer gas(es) to a first spaceresiding between the focus ring and the electrode, and a second spaceresiding between the substrate and the electrode, and controlling atemperature of the electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the invention will become moreapparent and more readily appreciated from the following detaileddescription of the exemplary embodiments of the invention taken inconjunction with the accompanying drawings, where:

FIG. 1 presents a schematic cross-section of a known substrate holderindicating a non-uniform plasma sheath;

FIG. 2A presents a schematic cross-section of an improved substrateholder according to an embodiment of the present invention;

FIG. 2B presents a schematic cross-section of an improved substrateholder according to another embodiment of the present invention;

FIG. 2C presents a schematic cross-section of an improved substrateholder according to another embodiment of the present invention;

FIG. 3 presents a flow diagram for a method of minimizing arcing betweena substrate and a focus ring according to a first embodiment of thepresent invention; and

FIG. 4 presents a flow diagram for a method of controlling substrate andfocus ring temperature according to a second embodiment of the presentinvention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention relates to a substrate holder employed in plasmaprocessing and more particularly to an improved substrate holder forplasma processing. According to the illustrated embodiment of thepresent invention depicted in FIG. 2A, an improved substrate holder 100can comprise an electrode 110, an insulating member 112 and a groundmember 114. A focus ring 118, comprising an upper surface 150, a lowersurface 152, an outer surface 154 at an outer diameter and an innersurface 156 at an inner diameter, is coupled to an upper surface 140 ofelectrode 110. The inner diameter of inner surface 156 of focus ring 118is sufficiently large to accommodate substrate 122 and to centersubstrate 122 about an axis of revolution 111 of electrode 118.Substrate 122 comprises an upper surface 160, a bottom surface 162, andan outer surface 164 at an outer diameter facing inner surface 156 offocus ring 118. Substrate 122 is coupled to electrode 110 in such a waythat bottom surface 162 of substrate 122 opposes upper surface 140 ofelectrode 110.

In order to preserve a uniform plasma sheath thickness 130 across boththe upper surface 150 of focus ring 118 and the upper surface 160 ofsubstrate 122 and, hence, a spatially homogeneous surface potential,focus ring 118 is designed and implemented as an electrical elementcomprising an RF impedance substantially similar to that of substrate122. In a first embodiment, focus ring 118 comprises, for example, atleast one of silicon and silicon carbide when processing a substrate 122comprising, for example, silicon. The material properties of focus ring118 are specifically chosen to produce a RF impedance for focus ring 118that is substantially equivalent to the RF impedance of substrate 122.Focus ring 118 can comprise material properties such that its inherentcapacitance, inductance and resistance are similar to that of substrate122. For example, focus ring 118 can comprise heavily doped siliconcarbide when processing a substrate 122 comprising silicon. In analternate embodiment, the upper surface 150 of focus ring 118 cancomprise a shape other than flat, such as, for example, an inclinedsurface as shown in FIGS. 2B and 2C. In an alternate embodiment (notshown), the upper surface 150 of focus ring 118 comprises at least oneof a convex and a concave surface. Furthermore, the thickness of focusring 118 is designed to be tailored to the thickness of substrate 122.The thickness of substrate 122 can be, for example, 750 micron. In oneembodiment, the focus ring has a thickness of 100 to 2000 microns. Inanother embodiment, the focus ring has a thickness substantiallyequivalent to the thickness of the substrate 122. Exemplary thicknessesof the focus ring include, but are not limited to, (1) a thicknesswithin 20% of the thickness of the substrate, (2) a thickness within 10%of the thickness of the substrate, (3) a thickness within 5% of thethickness of the substrate, and (4) a thickness within 1% of thethickness of the substrate. In an alternate embodiment, the thickness offocus ring 118 is substantially different than the thickness ofsubstrate 122.

Electrode 110 can be, for example, generally cylindrical comprising anouter surface 144 at an outer diameter and an axis of rotation 111.Additionally, electrode 110 can comprise aluminum and, therefore, it canbe anodized, hence, comprising an anodization layer 142, as depicted inFIG. 2A. Desirably, the outer diameter of outer surface 144 of electrode110 is substantially equivalent to outer diameter of outer surface 154of focus ring 118. In an alternate embodiment, the outer diameter ofouter surface 144 of electrode 110 is different than the outer diameterof outer surface 154 of focus ring 118.

Insulating member 112, can also be, for example, generally cylindricalcomprising an inner surface 145 at an inner diameter, an outer surface146 at an outer diameter and an axis of revolution 111. Desirably, theinner surface 145 corresponds to an inner diameter substantiallyequivalent to the outer diameter of outer surface 144 of electrode 110.Moreover, the inner diameter of inner surface 145 of insulating member112 can be substantially equivalent to the outer diameter of the outersurface 154 of focus ring 118. Therefore, insulating member 112 cancomprise an inner edge 190 substantially flush with the outer surface154 of focus ring 118 in order to serve as a means of centering focusring 118 about axis of revolution 111. In an alternate embodiment,insulating member 112 can comprise an inner surface 145 having an innerdiameter different than the outer diameter of outer surface 154 of focusring 118 and, therefore, allow an edge (or groove) 190 to be machinedwithin the upper surface of insulating member 112 in order to serve thecentering function described above. Preferably, insulating member 112comprises a dielectric material such as, for example, quartz or alumina.

Ground member 114 can also be, for example, generally cylindricalcomprising an inner surface 147 at an inner diameter, an outer surface148 at an outer diameter and an axis of revolution 111. Desirably, theinner surface 147 corresponds to an inner diameter substantiallyequivalent to the outer diameter of outer surface 146 of insulatingmember 112. Additionally, ground member 114 can comprise aluminum and,therefore, it can be anodized, hence, comprising an anodization layer116, as depicted in FIG. 2A.

Alternately, the substrate 122 can be, for example, affixed to thesubstrate holder 100 via an electrostatic clamp 120. Electrostatic clamp120 comprises a clamp electrode 121 connected to a high voltage (HV),direct current (DC) voltage source (not shown). Typically, the clampelectrode is fabricated from copper and embedded within a ceramicelement. The electrostatic clamp 120 can be operable in either amonopolar or bipolar mode; each mode is well known to those skilled inthe art of electrostatic clamping systems. Desirably, clamp electrode120 can serve as upper surface 140 of electrode 110 and extends underthe lower surface 152 of focus ring 118 and the lower surface 162 ofsubstrate 122. In one embodiment, electrostatic clamp 120 can beutilized to clamp both the focus ring 118 and the substrate 122. Inanother embodiment, electrostatic clamp 120 can comprise two or moreindependent clamp electrodes with separate HV DC voltage sources forindependently clamping the focus ring 118 and the substrate 122.

Alternately, electrode 110 can further include a cooling/heating systemincluding a re-circulating fluid that receives heat from substrate 122and focus ring 118 and transfers heat to a heat exchanger system (notshown) when cooling, or when heating, transfers heat from the heatexchanger system to the above elements. In other embodiments, heatingelements, such as resistive heating elements, or thermoelectricheaters/coolers can be included as part of the heating/cooling system.The heating/cooling system further comprises a device (not shown) formonitoring the electrode 110 temperature. The device can be, forexample, a thermocouple (e.g., K-type thermocouple).

Moreover, heat transfer gas can be delivered to at least one of a firstspace 170 between upper surface 140 of electrode 110 and lower surface152 of focus ring 118 using a first gas supply line 172, and a secondspace 180 between upper surface 140 of electrode 110 and lower surface162 of substrate 122 using a second gas supply line 182 (see FIG. 2A).Gas supply lines 172 and 182 can distribute heat transfer gas to one ormore orifices or a groove formed in the upper surface 140 of electrode110. The implementation of heat transfer gas distribution is well knownto those skilled in the art of substrate processing. The supply of heattransfer gas to the first space 170 can improve the gas-gap thermalconductance between the lower surface 152 of focus ring 118 and theupper surface 140 of electrode 110, while the supply of heat transfergas to the second space 180 can improve the gas-gap thermal conductancebetween the lower surface 162 of substrate 122 and the upper surface 140of electrode 120. The heat transfer gas can be, for example, at leastone of a Noble gas such as helium, argon, neon, xenon, krypton, aprocess gas such as C₄F₈, CF₄, C₅F₈, C₄F₆ and C₂F₆, or a mixturethereof. Therefore, controlling the temperature of electrode 110 via theaforementioned heating/cooling system can lead to control of both thetemperature of the focus ring 118 and the temperature of the substrate122. In one embodiment, the supply of heat transfer gas to the firstspace 170 is independent of the supply of heat transfer gas to thesecond space 180 using independent gas supplies 174 and 184 as shown inFIG. 2A. Using independent heat transfer gas supplies, the pressure infirst space 170 can be adjusted to be different than the pressure insecond space 180. In an alternate embodiment, gas supply lines 172 and182 are supplied heat transfer gas from a single heat transfer gassupply. In an alternate embodiment, the second space 180 is divided intoone or more spaces to which heat transfer gas is supplied independently.

Substrate 122 can be, for example, transferred into and out of a processchamber (not shown) through a slot valve (not shown) and chamberfeed-through (not shown) via robotic substrate transfer system where itis received by substrate lift pins (not shown) housed within substrateholder 100 and mechanically translated by devices housed therein.Therefore, lift pin holes (not shown) in electrode 110 and electrostaticclamp 120 accommodate the passage of lift pins to and from the lowersurface 162 of substrate 122. Once substrate 122 is received from thesubstrate transfer system, it is lowered to an upper surface 140 ofsubstrate holder 100.

In the illustrated embodiment, shown in FIG. 2A, electrode 110 can, forexample, further serve as a RF electrode through which RF power iscoupled to plasma in a processing region adjacent substrate 122. Forexample, electrode 110 is electrically biased at a RF voltage via thetransmission of RF power from a RF generator (not shown) through animpedance match network (not shown) to electrode 110. The RF bias canserve to heat electrons and, thereby, form and maintain plasma or toprovide a RF bias in order to enable control of ion energy at the uppersurface 160 of substrate 122. In this configuration, the system canoperate as a reactive ion etch (RIE) reactor, wherein the chamber servesas ground surfaces. A typical frequency for the RF bias can range from 1MHz to 100 MHz and is preferably 13.56 MHz. RF systems for plasmaprocessing are well known to those skilled in the art. Impedance matchnetwork topologies (e.g. L-type, π-type, T-type, etc.) and automaticcontrol methods are also well known to those skilled in the art.

Referring now to FIG. 3, a flowchart 300 describes a method ofprocessing a substrate using the improved substrate holder depicted inFIG. 2 in order to minimize the possibility of arcing between thesubstrate edge and the focus ring. The method begins with step 310wherein a focus ring 118 as described above is placed upon substrateholder 100 and coupled to the upper surface 140 of electrode 110. Thefocus ring 118 can, for example, be set atop the electrode 110 by anoperator during chamber maintenance. Furthermore, the focus ring 118 canbe centered about an axis of revolution 111 by aligning the outersurface 154 of focus ring 118 flush with the inner edge 190 ofinsulating member 112. Alternately, focus ring 118 can be received andlowered to the upper surface 140 of electrode 110 by a set of lift pins(not shown), wherein the focus ring 118 is transferred into and out ofthe chamber via the robotic substrate transfer system described above.

In step 320, substrate 122 is placed upon substrate holder 100 andcoupled to the upper surface 140 of electrode 110. The substrate 122can, for example, be received and lowered to the electrode 110 by a setof lift pins (not shown), as described above, wherein substrate 122 istransferred into and out of the chamber via the robotic substratetransfer system. Furthermore, substrate 122 can be centered about anaxis of revolution 111 by aligning the outer surface 164 of substrate122 flush with the inner edge 156 of focus ring 118.

In step 330, substrate 122 is processed in the plasma processing systemaccording to a process recipe. The process recipe can, for example,include setting the electrostatic clamping voltage (force), backside gaspressure (e.g. gas pressure in spaces 170 and 180), RF power toelectrode 110, chamber gas pressure, process gas partial pressure(s) andflow rate(s), etc.

Referring now to FIG. 4, a flowchart 400 describes a method ofprocessing a substrate using the improved substrate holder depicted inFIG. 2 in order to control the temperatures of focus ring 118 andsubstrate 122. The method begins with step 410 wherein, as before, afocus ring 118 as described above is placed upon substrate holder 100and coupled to the upper surface 140 of electrode 110. The focus ring118 can, for example, be set atop the electrode 110 by an operatorduring chamber maintenance. Furthermore, the focus ring 118 can becentered about an axis of revolution 111 by aligning the outer surface154 of focus ring 118 flush with the inner edge 190 of insulating member112. Alternately, focus ring 118 can be received and lowered to theupper surface 140 of electrode 110 by a set of lift pins (not shown),wherein the focus ring 118 is transferred into and out of the chambervia the robotic substrate transfer system described above.

In step 420, substrate 122 is placed upon substrate holder 100 andcoupled to the upper surface 140 of electrode 110. The substrate 122can, for example, be received and lowered to the electrode 110 by a setof lift pins (not shown), as described above, wherein substrate 122 istransferred into and out of the chamber via the robotic substratetransfer system. Furthermore, substrate 122 can be centered about anaxis of revolution 111 by aligning the outer surface 164 of substrate122 flush with the inner edge 156 of focus ring 118.

In step 430, a voltage supplied from a HV, DC voltage source is appliedto electrostatic clamp 120 in order to provide a clamping force betweenthe focus ring 118 and electrode 110 as well as the substrate 122 andelectrode 110. In step 440, once the focus ring 118 and substrate 122are clamped, a heat transfer gas can be supplied to the first and secondspaces 170, 180 described above in order to improve the gas-gap thermalconductance between the focus ring 118 and electrode 110, and thesubstrate 122 and the electrode 110. In an embodiment of the presentinvention, the gas pressure in first space 170 is substantiallyequivalent to the gas pressure in second space 180. In an alternateembodiment, the gas pressure in first space 170 is substantiallydifferent than the gas pressure in second space 180.

In step 450, the temperature of electrode 110 is controlled via theheating/cooling system described above, thereby providing temperaturecontrol for the focus ring 118 and the substrate 122.

Although only certain exemplary embodiments of this invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention.

1. An improved substrate holder for plasma processing, the improvement comprising: a focus ring, said focus ring surrounding a substrate wherein a thickness of said focus ring is substantially equivalent to a thickness of said substrate; an electrode, said electrode is capable of supporting said substrate and said focus ring on an upper surface thereof; an insulating member, said insulating member surrounding said electrode; and a ground member, said ground member surrounding said insulating member.
 2. The improvement according to claim 1, wherein said upper surface of said electrode further comprises at least one electrostatic clamp for clamping at least one of said focus ring and said substrate to said electrode, said at least one electrostatic clamp comprises a clamp electrode embedded within a ceramic member near said upper surface of said electrode, said clamp electrode extending below at least one of said focus ring and said substrate.
 3. The improvement according to claim 1, wherein said insulating member is further capable of centering said focus ring.
 4. The improvement according to claim 1, wherein said electrode is RF biasable.
 5. The improvement according to claim 1, wherein said electrode is temperature controllable.
 6. The improvement according to claim 2, wherein a space extending between said focus ring and said substrate, and said electrostatic clamp is supplied with a heat transfer gas.
 7. The improvement according to claim 6, wherein said heat transfer gas comprises at least one of helium, argon, neon, xenon, krypton, C₄F₈, CF₄, C₅F₈, and C₂F₆.
 8. The improvement according to claim 1, wherein said substrate comprises a silicon wafer.
 9. The improvement according to claim 1, wherein said focus ring comprises at least one of silicon and silicon carbide.
 10. The improvement according to claim 1, wherein said insulating member comprises at least one of quartz and alumina.
 11. The improvement according to claim 1, wherein said ground member comprises at least one of anodized aluminum and aluminum.
 12. The improvement according to claim 1, wherein said thickness of said focus ring ranges from 100 micron to 2000 micron.
 13. The improvement according to claim 1, wherein said thickness of said focus ring is within 20% of said thickness of said substrate.
 14. The improvement according to claim 1, wherein said thickness of said focus ring is within 10% of said thickness of said substrate.
 15. The improvement according to claim 1, wherein said thickness of said focus ring is within 5% of said thickness of said substrate.
 16. The improvement according to claim 1, wherein said thickness of said focus ring is within 1% of said thickness of said substrate.
 17. An improved substrate holder for plasma processing, the improvement comprising: a focus ring, said focus ring surrounding a substrate wherein a RF impedance of said focus ring is substantially equivalent to a RF impedance of said substrate; an electrode, said electrode is capable of supporting said substrate and said focus ring on an upper surface thereof; an insulating member, said insulating member surrounding said electrode; and a ground member, said ground member surrounding said insulating member.
 18. A method of minimizing arcing between a substrate and a focus ring during plasma processing, the method comprising the steps of: placing a focus ring on an electrode, said focus ring centered about an axis of revolution of said electrode by an insulating member, said insulating member surrounding said electrode; placing a substrate on an electrode, said substrate centered about said axis of revolution of said electrode by said focus ring; and plasma processing said substrate utilizing a process recipe.
 19. A method of controlling a temperature of a substrate and a focus ring, the method comprising the steps of: placing a focus ring on an electrode, said focus ring centered about an axis of revolution of said electrode by an insulating member, said insulating member surrounding said electrode; placing a substrate on an electrode, said substrate centered about said axis of revolution of said electrode by said focus ring; clamping at least one of said focus ring and said substrate to said electrode using an electrostatic clamp, wherein said electrostatic clamp is fabricated within an upper surface of said electrode; supplying a heat transfer gas to a first space between said focus ring and said electrode, and a second space between said substrate and said electrode; and controlling the temperature of said electrode.
 20. The method as claimed in claim 19, wherein the step of clamping comprises clamping said focus ring and said substrate to said electrode using the same electrostatic clamp.
 21. The method as claimed in claim 19, wherein the step of clamping comprises clamping said focus ring and said substrate to said electrode using different electrostatic clamps. 